1. Field of the Invention
The present invention relates to a variable-speed controlling device which calculates an AC (Alternating Current) voltage instruction value by using a primary angular frequency instruction value and a secondary magnetic flux instruction value, and drives an induction motor by providing this voltage instruction value to a power converting circuit such as an inverter, etc.
2. Description of the Related Art
FIG. 1 is a block diagram showing the whole of a conventional variable-speed controlling device for use with an induction motor.
In this figure, a voltage instruction value calculating circuit 4 calculates voltage instruction values v1d* and v1q* in a rotating coordinate system (d-q axes) based on a primary angular frequency instruction value xcfx891* and a secondary magnetic flux instruction value xcfx862*, which are output from an instruction value generating circuit 3, and outputs the calculated values. Next, an integrator 5, to which xcfx891* is input, calculates a phase angle instruction value xcex8*.
Here, assume that the rotating coordinate system rotates at an angular velocity equal to the primary angular frequency instruction value xcfx891*, its d-axis is a coordinate axis matching the direction of the phase angle instruction value xcex8*, and its q-axis is a coordinate axis orthogonal to the d-axis.
A coordinate transforming circuit 7, to which the voltage instruction values v1d* and v1q* are input, performs a rotating coordinate transformation according to the phase angle instruction value xcex8*, and outputs an AC voltage instruction value vector v1*. A power converting circuit 1 such as an inverter, etc. outputs an AC voltage of each phase according to the AC voltage instruction value vector v1*, and drives an induction motor 2.
In the above described conventional variable-speed controlling device, a discrepancy may sometimes occur between a secondary magnetic flux instruction value xcfx862* determined according to the direction of the phase angle instruction value xcex8* and the secondary magnetic flux occurring in the induction motor 2, due to a calculation error in the voltage instruction value calculating circuit 4, an error between the instruction value of the AC voltage output from the power converting circuit 1 and an actual value, or the like.
As a result, the magnetic flux according to an instruction value cannot be generated, which leads to a decrease in generated torque or in a motor efficiency, etc.
An object of the present invention is to provide a variable-speed controlling device for use with an induction motor, which comprises a means for compensating for the discrepancy between a secondary magnetic flux instruction value and a secondary magnetic flux actually occurring in an induction motor, realizes a satisfactory control by generating the secondary magnetic flux according to the instruction value, and can generate desired torque and improve a motor efficiency, so as to overcome the above described problems.
The variable-speed controlling device according to the present invention, for use with an induction motor, is configured to comprise a voltage instruction value calculating unit, an integrating unit, a power converting circuit, a current detecting unit, a voltage detecting unit, an induced voltage calculating unit, a primary angular frequency compensation amount calculating unit, and a compensating unit.
In a first aspect of the present invention, the voltage instruction value calculating unit calculates an AC voltage instruction value on d-q axes rotating coordinates rotating at an angular velocity equal to a primary angular frequency instruction value by using the primary angular frequency instruction value and a secondary magnetic flux instruction value. The integrating unit calculates a phase angle instruction value by integrating the primary angular frequency instruction value. The power converting circuit performs power conversion according to the AC voltage instruction value obtained from the AC voltage instruction value and the phase angle instruction value, and supplies an AC voltage to the induction motor. The current detecting unit detects the current of the induction motor. The induced voltage calculating unit calculates the d-axis component of the induced voltage vector of the induction motor from the AC voltage instruction value vector, the output of the current detecting unit, a first primary angular frequency instruction value, and a motor constant. The primary angular frequency compensation amount calculating unit calculates a primary angular frequency compensation amount from the first primary angular frequency instruction value and the calculation result of the d-axis component of the induced voltage vector from the induced voltage calculating unit. The compensating unit generates a second primary angular frequency instruction value provided to the voltage instruction value calculating unit and the integrating unit by adding the primary angular frequency compensation amount to the first primary angular frequency instruction value.
In a second aspect of the present invention, the voltage instruction value calculating unit calculates an AC voltage instruction value on d-q axes rotating coordinates rotating at an angular velocity equal to the primary angular frequency instruction value by using the primary angular frequency instruction value and the secondary magnetic flux instruction value. The integrating unit calculates a phase angle instruction value by integrating the primary angular frequency instruction value. The power converting circuit performs power conversion according to the AC voltage instruction vector obtained from the AC voltage instruction value and the phase angle instruction value, and supplies an AC voltage to the induction motor. The current detecting unit detects the current of the induction motor. The voltage detecting unit detects the terminal voltage of the induction motor. The induced voltage calculating unit calculates the d-axis component of the induced voltage vector of the induction motor from the output of the voltage detecting unit, the output of the current detecting unit, the first primary angular frequency instruction value, and the motor constant. The primary angular frequency compensation amount calculating unit calculates the primary angular frequency compensation amount from the first primary angular frequency instruction value and the calculation result of the d-axis component of the induced voltage vector from the calculation of the induced voltage calculating unit. The compensating unit generates the second primary angular frequency instruction value provided to the voltage instruction value calculating unit and the integrating unit by adding the primary angular frequency compensation amount to the first primary angle frequency instruction value.